AGOURA HILLS — The dread of high school algebra is lost here amid the blue glow of computer screens and the clickety-clack of keyboards.

A fanfare plays from a speaker as a student passes a chapter test. Nearby, a classmate watches a video lecture on ratios. Another works out an equation in her notebook before clicking on a multiple-choice answer on her screen.

Their teacher at Agoura High School, Russell Stephans, sits at the back of the room, watching as scores pop up in real time on his computer grade sheet. One student has passed a level, the data shows; another is retaking a quiz.

“Whoever thought this up makes life so much easier,” Stephans says with a chuckle.

This textbook-free classroom is by no means the norm, but it may be someday. Slowly, but in increasing numbers, grade schools across the country are supplementing or substituting the heavy, expensive and indelible hardbound book with its lighter, cheaper and changeable cousin: the digital textbook.

Also known as a flexbook because of its adaptability, a digital textbook can be downloaded, projected and printed, and can range from simple text to a Web-based curriculum embedded with multimedia and links to Internet content. Some versions must be purchased; others are “open source” — free and available online to anyone.

Hardbound books still dominate the $7 billion U.S. textbook market, with digital textbooks making up less than 5 percent, according to analyst Kathy Mickey of Simba Information, a market research group.

But that is changing, as K-12 schools follow the lead of U.S. universities and schools in other countries, including South Korea and Turkey. In Florida’s Broward County, students and teachers log online to access digital versions of their Spanish, math and reading books. In Arizona, classes at one Vail School District high school are conducted entirely with laptops instead of textbooks. And in Virginia this year, state officials and educators unveiled a free physics flexbook to complement textbooks.

California made the largest embrace of digital textbooks this summer when it approved 10 free high school math and science titles developed by college professors and the CK-12 Foundation, a Palo Alto-based nonprofit aimed at lowering the cost of educational materials. The titles were approved as meeting at least 90 percent of California’s academic standards, with the state leaving the choice to use them up to individual schools.

Gov. Arnold Schwarzenegger, hopes they will. His digital textbook initiative is meant to cut costs in the severely cash-strapped state. Given that the average textbook costs $100, he argued, the state could save $400 million if its 2 million high school students used digital math and science texts. The initiative also aims to replace aging hardbound books that don’t teach students about the Iraq war, the country’s first black president or the Human Genome Project.

“The textbooks are outdated, as far as I’m concerned, and there’s no reason why our schools should have our students lug around these antiquated and heavy and expensive books,” Schwarzenegger said this summer. “Digital textbooks are good not only for the students’ achievement, but they’re also good for the schools’ bottom line.”

California public and private schools spent more than $633 million on textbooks in 2007, making the state the biggest spender nationwide, according to the latest data from the Association of American Publishers. Schools in Texas spent $375 million; in New York, $264 million. The District of Columbia spent $13.9 million.

Schools using digital texts say it’s too soon to tell how much money they may be saving. As critics point out, long-term fiscal benefits require upfront resources that many schools lack: money, teacher training, bandwidth to support Internet multimedia and, most critically, computers.

The majority of households have personal computers and Internet access, according to a 2005 report from the Census Bureau, but access declines with income. And U.S. schools on average have roughly one computer for every four students, according to 2005 data from the National Center for Education Statistics.

“It’s going to be a bit of a challenge for schools throughout the country to implement this new technology,” said David Sanchez, president of the California Teachers Association. “How do you guarantee all children have access to that kind of textbook?”

Glen Thomas, California’s education secretary, questions whether digital textbooks require a computer for every child. “This initiative is not about hardware,” he said. “I visited a classroom where there were a couple kids using laptops, several had textbooks, some had a couple chapters printed out, and the lesson was displayed on a screen in front of the class.”

For now, it appears that digital textbooks are largely a school-by-school, teacher-by-teacher choice. But converts such as Stephans of Agoura High School are quick to encourage more.

“If there was a list of math teachers who would have signed up for this, I would have been at the bottom,” said Stephans, who hesitantly agreed to pilot the textbook-free class this year. To educators considering the digital possibilities, he now says: “What are you waiting for?”

Otto Warmbier was arrested in January 2016 at the end of a brief tourist visit to North Korea. He had been medically evacuated and was being treated at the University of Cincinnati Medical Center when he died at age 22.